Sure it would be nice to build a war chest of miles in one airline, but as someone else mentioned, it's probably best not to put all your eggs in one basket. Having said that, what is a good asset allocation of miles across different airlines or different alliances? I assume it will be very difficult to do 33% across carriers on 3 major alliances and maintain elite status on each airline. I would imagine a 50/30/20 would be a reasonable divide, with a very frequent traveller maintaining top elite status on one airline, then mid-tier on a 2nd airline and lower tier on the 3rd airline with equivalent amount of miles in each account. Even this would be difficult unless he/she is travelling heavily for work. A more reasonable one would be to maintain mid-tier elite in the primary airline and the lower tier on the secondary airline and no status on the 3rd, but still accumulating enough miles through flying, credit cards, other bonuses.